1. Field of the Invention
The present invention relates to a device for supporting the focus adjustment of a lens apparatus and a method for adjusting the focus of the lens apparatus.
2. Description of the Related Art
Recently, in stores used in the finance business and retail business and the like, there has been often used a surveillance camera which is composed of a CCD or the like. Especially, there has been increasing the need for a dome-type surveillance camera system (which is hereinafter referred simply to as a surveillance camera) which includes a dome-shaped case member for the purpose of not only protecting a lens apparatus but also covering up the image pickup direction thereof.
The structure of this type of surveillance camera is disclosed in JP-2000-305138, JP-2001-45344 and the like. That is, the surveillance camera has a dome-shaped appearance; and, it also includes a base member, a camera apparatus having a lens apparatus to be mounted on the base member, and a light transmissible case member to be mounted on, for example, the base member. The lens apparatus includes a mechanism which can be rotated on the base member in the horizontal direction and/or in the vertical direction. The lens apparatus, which is mounted on this type of surveillance camera, incorporates therein a single focus lens, a variable focus lens and the like. The reason for this is that, according to the surveillance range and installation condition of the lens apparatus, the focus and/or focal distance (zoom) thereof can be set properly. Therefore, the lens apparatus includes adjusting means for manually adjusting the focus and/or focal distance of the lens apparatus and thus, when the surveillance camera is installed, the focus and/or focal distance of the lens apparatus must be adjusted. By the way, the case member is made of plastic material such as acryl having a thickness of the order of several millimeters and is mounted on, for example, the base member in such a manner that it covers at least the image pickup range of the lens apparatus and the adjusting means of the lens apparatus.
A method for installing this type of surveillance camera is disclosed in JP-2000-209471 and the like. Specifically, when installing the surveillance camera, it is installed on the ceiling, wall surface and the like of a store, while the optical axis of the lens apparatus is set in a given direction in the horizontal and/or vertical direction. And, in a state where the case member is not mounted, the focus and/or focal distance of the lens apparatus is manually adjusted using the built-in adjusting means: that is, after the focus and/or focal distance of the lens apparatus is adjusted sufficiently, the case member is mounted onto the surveillance camera and the surveillance camera is installed, which completes the installation of the surveillance camera.
However, in the above-mentioned conventional structure, in some cases, the optical path length of an object light varies between a state where the case member is not mounted on the surveillance camera and a state where the case is mounted on the surveillance camera, thereby causing image forming positions to vary between these two states. When making the focus adjustment again for the purpose of correcting such variation in the image forming position, since the adjusting means provided in the lens apparatus is covered by the case member, it is necessary that the case member is removed from the lens apparatus and, after then, the focus and focal distance of the lens apparatus are manually adjusted. Also, to attain the sufficient focus and focal distance adjustment, in some cases, the manual focus adjustment and the mounting/removal of the case member must be carried out repeatedly several times in a trial-and-error manner. This complicates the focus adjustment of the lens apparatus greatly, which raises a problem that the installation of the surveillance camera itself is difficult.